A light emitting diode (LED) is a semiconductor device which is activated by current to generate light of various colors. The III-V compound semiconductors, such as gallium nitride (GaN), which have wide band gap, high luminous efficiency, high electron saturation drift velocity, and stable chemical properties, have great application potential in high-brightness blue light emitting diodes, blue laser and other optoelectronic devices areas, and have aroused wide attention.
However, semiconductor light emitting diodes have low luminous efficiency in the prior art. As for light emitting diodes without package, the luminous efficiency is only a few percent. A lot of energy inside the device can not be sent out, thereby not only causing energy waste, but also affecting lifetime of the device. Therefore, it is of key importance to improve the luminous efficiency of semiconductor light emitting diodes.
Because of the above application requirements, a plurality of methods for improving the luminous efficiency of semiconductor light emitting diodes have been applied in device structure, for example, surface roughness, Metal reflector structure, and so on. Chinese patent publication No. CN1858918A discloses a kind of light emitting diodes and the under surface of the light emitting diodes forms an omnidirectional reflector structure, whereby the luminous efficiency of the light emitting diodes is improved. However, the method disclosed in this prior art needs to form a film comprising a plurality of high refractive index layers and low refractive index layers stacked on the substrate, of which the manufacturing process is very complex.